shell fractal

Using Variables in Remote PowerShell Sessions

Q: I'm trying to invoke commands on a remote server in PowerShell, but any variables I try to use are failing. What can I do?

A: PowerShell variables are great for storing information that's available within the PowerShell session. For example:

$message = "Message to John"
write-host $message

would output the text contained in the $message variable with no problem. Now consider running the same command on a remote machine:

$message = "Message to John"
Invoke-Command -ComputerName savdalhv20 -ScriptBlock {write-host $message}

Nothing shows in the output. The reason for this is that Invoke-Command creates a new PowerShell session on the remote machine that doesn't have the variables you defined locally available and therefore contains no data.

If you want to use variables in a remote session, such as with Invoke-Command, you need to pass those variables as parameters to the script block that will be used with Invoke-Command and then the actual value as an argument. For example:

$message = "Message to John" 
$ScriptBlockContent = { 
    param ($MessageToWrite)
    Write-Host $MessageToWrite }

Invoke-Command -ComputerName savdalhv20 -ScriptBlock $ScriptBlockContent -ArgumentList $message

This now works; the text in the message is output to the screen. This is because the code being run remotely via Invoke-Command is writing a variable, $MessageToWrite, which is expected as a parameter when used and is populated with the value of $message via the -ArgumentList. Therefore, when you want to use variables that are defined locally, you must pass them as parameters to the remote session.

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